Kinetoplastea Trypanosomatidae are unicellular flagellated parasites of different kind of hosts. They cause diseases in plants, animals and humans. These parasites are transmitted by insect vectors in a wide range of geographic areas. In this communication we review the interactions between trypanosomatid parasites, their hosts and thoughts about their impact on environmental health, especially in those regions where hosts are natural reserves of many species. The interactions of these parasites and their hosts in some cases have great economic and environmental impact. We also address the genetic mechanisms that determine variability in some specific taxa. Two cell fusion and recombination of nuclear genomes and mitochondrial introgression seems to be the mechanisms that produce the greatest variability. However, these organisms most frequently reproduce clonally. Finally the mechanisms of the trypanosomatids response to environmental changes in their host are also analyzed.